Modelling African Horse Sickness in South Africa

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What is the research about?

The purpose of this research was to model the spread of African horse sickness (AHS) in populations of plain zebra in the Western Cape Province in order to feedback information to the South African horse industry on the potential of these populations to act as a wildlife reservoir of virus in the control and surveillance areas.

This research addresses three main objectives relevant to Western Cape Province and the understanding of AHS spread in plain zebra:

1.  Assess the high-risk period in which AHS will circulate persistently in Western Cape Province zebra population
2. Evaluate the risk of each holding in Western Cape Province to generate widespread and persistent circulation of AHS in zebra
3. Assess the required size of a zebra population to allow persistent circulation of AHS in Western Cape Province

Key findings

The results of this work provided an improved understanding of how AHS virus spread in this wildlife population, particularly it clarified conditions in which incursions would persist and become endemic in zebra. Particularly, our results showed that:

• The population of plain zebras currently present in Western Cape Province are not sufficiently large for AHS incursion events to become endemic;
• The coastal populations in Western Cape Province need to be >2500 individuals for AHS to persist >2 years, even if zebras are infectious for more than 50 days, on average;
• AHS cannot become endemic in the coastal population of Western Cape Province unless the zebra population involves at least 50,000 individuals;
• Inland populations of plain zebra in Western Cape Province may represent a risk for AHS to persist but would require a population of at least 500 zebras or show unrealistic duration of infectiousness for AHS incursion events to become endemic.

Selected publications

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